Your DKIM signature is not validDomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message.The DKIM signature of your message is:

We were not able to retrieve your public key.Please ensure that you inserted your DKIM TXT DNS record on your domain exmaple.com using the selector mail.If you recently modified your DNS, please be patient and test again your Newsletter in 12 hours, it may take some time for the DNS to be propagated

But I have the key added and Enabled DKIM support. Please check the below screenshot. What should I do now?